The patient was admitted to hospital in Hong Kong on Wednesday, the authority said. It wasn't immediately clear how or where he contracted the virus.
He had said he hadn't had any recent exposure to poultry or wet markets, according to the Centre for Health Protection.
Hong Kong has confirmed three human cases of H7N9 in three weeks as fears grow over the spread of the disease in South Korea, Japan and China.
All three patients in Hong Kong had visited southern China. The second case was confirmed last Friday, while the first patient died from H7N9 on Christmas Day.
In mainland China, H7N9 has killed at least four people this season, with the latest death reported in the eastern province of Shandong on Thursday. At least 19 infections have been confirmed.
China saw its last major bird flu outbreak in late 2013 and early 2014, when 36 patients died and the agricultural sector suffered more than $6 billion in losses.
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